(a) Field of the Invention
The present invention relates to an automatic transmission, and more particularly, to a powertrain of an automatic transmission.
(b) Description of the Related Art
A multi-stage gearshift mechanism of an automatic transmission includes a plurality of planetary gear sets. A powertrain having such a plurality of planetary gear sets varies the torque in multi-stages and outputs it to an output shaft when receiving a converted engine torque from a torque converter. The more speeds the powertrain of an automatic transmission has, the better the power performance and fuel consumption. Therefore, it is desirable for powertrains to have as many speeds as possible. Even for the same number of speeds, durability, power transmission efficiency, and size/weight of a transmission are substantially dependent on how planetary gear sets are arranged. Therefore, research for greater structural strength, less power loss, and more compact packaging is continuously being conducted.
For a manual transmission, too many speeds cause a driver the inconvenience of excessive manual shifting. However, for an automatic transmission, a transmission control unit automatically executes shifting by controlling the operation of the power train, and therefore, more speeds usually implies greater advantages.
Accordingly, research of four-speed and five-speed powertrains has been undertaken, and recently, a powertrain of an automatic transmission enabling six forward speeds and one reverse speed has been developed. On the other hand, a development for the automatic transmission which can realize more speed implies greater advantages.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.